The present invention relates generally to turbines and particularly relates to a seal for sealing adjacent downstream edges of transition pieces which extend between combustors and the first-stage turbine inlet of a gas turbine.
In conventional gas turbines, a compressor supplies compressed air under relatively high pressure to a plurality of combustors where fuel is burned to produce a high-temperature energetic flow of gas to drive a turbine. The turbine, in turn, may drive the compressor and also turn an output shaft, for example, for the generation of electricity.
More particularly, the combustors comprise a plurality of generally cylindrical can-like housings having fuel nozzles and arranged in a spaced annular array. Transition pieces are similarly arranged in an annular array for directing the flow of hot combusted gases from the combustors to the first stage turbine inlet. These transition pieces have generally cylindrical upstream inlet openings for receiving the gases of combustion directly from the correspondingly shaped combustors and are configured over their lengths such that their downstream ends comprise arcuate segments opening into the turbine inlet. The aggregate of these downstream openings forms an annulus for flowing energetic gases to the first stage of the turbine. Consequently, the transition pieces direct the flow of energetic gases from spaced, generally cylindrical, discrete upstream configurations to arcuate segments forming a downstream annular configuration whereby a substantially annular flow of energetic gases is provided the first-stage turbine inlet.
The side edges of the arcuate segments of the transition pieces at their downstream ends are typically mechanically sealed one to the other to prevent loss of compressor air. For example, radial seals for this purpose are described and illustrated in U.S. Pat. No. 4,465,284, of common assignee herewith. However, seals of this type have demonstrated significant wear problems. The inherent weight of the seal disclosed in that patent has, to some extent, aggravated the wear problem by imposing greater impact forces on adjacent transition pieces due to vibration. While reducing the wear of the seals has been attempted, it has not been particularly successful.
The wear problem for the transition piece seal is in part caused by combustor noise which drives the sheet metal of the transition piece into vibratory modes in multiple directions. Rather than attempt to reduce the wear problem by substituting materials less prone to wear as previously attempted, the present invention provides a flexibility and resiliency to the seals to essentially absorb the vibratory motion in its multiple directions, i.e., axially, radially and circumferentially.
According to the present invention, there is provided a flexible resilient seal for engaging adjacent, substantially radially extending edges of the transition pieces at their downstream ends directly upstream of and adjacent to the first-stage inlet of the turbine. The seal comprises a pair of spring clips secured in back-to-back relation one to the other and adapted to receive respective edge portions, i.e., radially extending circumferentially or transversely directed flanges of the adjacent transition pieces. The vibratory movement of the adjacent transition pieces is thus absorbed by the spring clips, while substantially simultaneously the spring clips provide an effective seal between the adjacent edge portions of the transition pieces. More particularly, the spring clips each comprise a base portion having a pair of arcuate, generally elongated spring segments, spaced one from the other and extending from opposite edges of the base portion and to one side thereof. The segments of each pair extend radially and are axially spaced from one another for receiving the circumferentially directed and radially outwardly projecting flange of the associated transition piece. This flange engages the spring clip segments adjacent their free distal ends. The spring clip segments therefore permit vibratory movement of the transition piece in the axial, circumferential and radial directions, while maintaining the seal between the clip and the flange.
Preferably, the spring clips are formed from a single elongated sheet of metal which is folded substantially intermediate its length about a pair of foldlines back onto itself to define a central section and sections underlying the central section. The underlying sections are reversely folded such that the spring clips extend at right angles from the central and underlying sections. The spring clips are thus disposed in back-to-back relation one to the other. By folding the single sheet of material in this manner, the central section and the underlying sections define a slot which receives a leaf spring. This leaf spring mounts the seal to a turbine inlet nozzle support ring. The leaf spring is generally U-shaped, and has one leg inserted into the slot of the seal spring. The opposite leg has a turned end forming a flange for receiving a bolt whereby the leaf spring can be secured to the nozzle support ring. With the spring clips extending in a radial direction, the flanges of the transition pieces are received between the arcuate spring segments. Hence, the transition pieces are free to absorb vibratory movement in the axial, circumferential and radial directions of the turbine.
In a preferred embodiment according to the present invention, there is provided a seal for substantially sealing spaced edge portions of adjacent turbine transition pieces comprising a pair of spring clips adapted to receive respective edge portions of adjacent turbine transition pieces, the spring clips being joined one to the other and enabling relative vibratory movement of the adjacent edge portions of the transition pieces while simultaneously providing a substantial seal between the adjacent edge portions to substantially preclude leakage flow of air therebetween.
In a further preferred embodiment according to the present invention, there is provided a turbine having transition pieces for flowing gases from a plurality of circumferentially spaced combustors to a first-stage turbine inlet wherein the transition pieces are configured to shape the gas flows from the combustors from generally cylindrical configurations at their upstream ends to arcuate segments at their downstream ends, a seal for substantially sealing spaced edge portions of adjacent turbine transition pieces at their downstream ends including a pair of spring clips engaging respective downstream edge portions of adjacent turbine transition pieces, the spring clips being joined one to the other to enable relative vibratory movement of the adjacent edge portions of the adjacent transition pieces while simultaneously providing a substantial seal between the adjacent edge portions to substantially preclude leakage flow of air therebetween.
Accordingly, it is a primary object of the present invention to provide a novel and improved seal for transition pieces between the combustors and the first-stage turbine inlet in a gas turbine which greatly increases the wear life of the seal by affording compliance to the movement and vibration of the transition pieces. It is also an object of the present invention to provide a mounting spring which enables mounting of the transition piece seal to the first-stage nozzle support ring, allowing further movement and compliance of the transition piece seal, a flexible attachment to the turbine, and in case of spring seal failure, prevention of foreign object damage in the turbine.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.